This is some initial error handling support which I am sure is likely to change
one all of the operations are ported to handlers. Prior to this though we were
simply swallowing the exception. The client would hang indefinitely waiting for
a response, making debugging difficult. With this we are propagating the stack
trace back to the client which should really help with debugging errors.

When a request is created, a new FilterHandler is registered on the event bus.
A FilterHandler wraps a Filter object. The operation response is sent back on
the event bus after the filter has been applied to all of the rows.
This commit adds filter support to SliceHandler. I will add support in GetHandler
in my next commit. Then I need to see about minimizing some of the json object
creation/mapping overhead.